In his first-ever interview, the sole Australian survivor of the Waco siege has revealed to 60 Minutes what really took place during the 51-day stand-off, and why he believes crazed cult leader David Koresh will one day return to Earth as the son of God.

Mystery over Rye Hunt's final movements lifted as family prepare to fly ashes home

Dehydration drove Australian backpacker Rye Hunt into attempting a drug-induced 800m swim that cost him his life, Brazilian police claim.

Hunt's body was discovered last week washed ashore on the idyllic Guaratiba beach, 50 kilometres from the centre of Rio de Janeiro.

The badly decomposed body, discovered by locals, meant it was difficult to ascertain how Hunt had died, after he had mysteriously vanished for almost three weeks.

Today, Brazilian investigators confirmed the 25-year-old Tasmanian had died of dehydration or drowning after suffering a psychotic episode from hallucinogenic drugs he had taken.

"The location of the body supports the investigation that Rye went to the island of Cotunduba during a psychotic episode, coherent with the state of someone who is running away from a danger created in their minds," police woman Elen Souto told ABC.

"Certainly because of his physical debilitation, probably because of dehydration, he must have tried to leave the island and not have had enough strength or health to get to land."

Dental records were required to identify the missing Australian, and his body has now been released to family who now face the ordeal of bringing Hunt home.

In a statement Hunt's family described how he had expressed a wish to be cremated and have his ashes scattered in Tasmania.

Hunt went missing after he separated from his travelling companion Mitchell Sheppard following an argument after the two had taken what is suspected to be a highly potent hallucinogen known as NBOMe.